Thermoplastic polyurethane elastomers (TPPUE) may be described as multiblock copolymers of general structure represented by (A-B).sub.n, where A and B are hard and soft segments, respectively, and n is &gt;1, typically &gt;10 and often &gt;100. TPPUEs are prepared from mixtures of diisocyanates, diols, and, often, low molecular weight polyol or polyamine chain extenders, which after reaction yield the multiblock copolymers. TPPUEs also may be prepared from diisocyanates, polyester or polyether diols or diamines, and low molecular weight polyols, polyamines, or mixtures of polyols and polyamines. The soft segment (B) typically results from a polyether or polyester diol component while the hard segment (A) typically results from the diisocyanate component. A book, Polyurethane Elastomers, by C. Hepburn (Applied Science, London, 1982), particularly Chapter 9 therein, broadly describes TPPUEs of the type related to the invention.
The known TPPUEs and blends containing TPPUEs all suffer some drawbacks in one or more properties, including mechanical properties, color stability to heat and light, clarity, and useful heat distortion properties. For example, in TPPUEs, the hard segments tend to agglomerate to form glassy and semi-crystalline phases in an elastomeric matrix of the soft segments, often leading to microphase separation (often termed "nacreous effect") due to incompatibility between, for example, polyether or polyester soft (B) segments and the hard urethane or urea (A) blocks. Phase separation becomes visually obvious when the elastomers are dyed or pigmented. The occurrence of phase separation is disclosed, for example, in U.S. Pat. No. 4,179,479, wherein polymeric blends are prepared from acrylonitrile/butadiene/styrene ("ABS") graft copolymers, high molecular weight (500,000 to 1,500,000) acrylate polymers and thermoplastic polyurethanes. All of the '479 patent compositions showed evidence of the nacreous effect and poor low and room temperature mechanical properties. Phase-separated materials also generally show poor tear resistance; hence, molded articles with reduced wall thickness, such as ski boot fastenings, do not possess sufficient toughness to withstand severe stress conditions. Another problem is achieving toughness above about 40M Pascal in TPPUEs or known TPPUE blends, and attempts to improve one property, such as toughness, often lead to degeneration of another property. For example, an attempt to improve the mechanical properties of TPPUEs (German Offenlegungsschrift 2,854,409) led to TPPUEs from a combination of polyester diols and diisocyanates, chain extended with 1,4-butane diol; the resulting TPPUEs had increased hardness and modulus but poor low temperature impact properties and evidence of extensive phase separation. Another attempt to prepare high modulus elastomer (German Offenlegungsschrift 2,854,407) wherein the elastomers described were melt processable blends of TPPUE's, based on polyethers or polyesters, urethanes and a graft copolymer consisting of a 95 to 65 weight percent rubbery core and a 35 to 5 wt. % hard shell, yielded mechanical properties of their blends which were compromised by severe phase separation.
Achieving good color stability also has been a problem in TPPUE blends. For example, in EP 12,343, the described elastomers were prepared from high molecular weight polyethylene oxide, polypropylene oxide ether diols, and diisocyanates. In spite of the fact that final product compositions were stabilized by the incorporation of thermoplastic graft copolymers, the resulting elastomers exhibited a yellow tinge characteristic of thermal instability and also showed poor low temperature impact and tensile modulus. Achieving good clarity in TPPUE blends has been another problem in the art, related to the nacreous effect, mentioned above, and to other factors. For example, German patent application, DE3925635-A, discloses ternary blends comprising polycarbonate based on 1,1-bis-4-hydroxyphenyl-cycloalkane, thermoplastic polyurethane and vinyl monomer-rubber graft copolymer. The blend compositions are reported to possess favorable balances of processing characteristics and physical and mechanical properties, but the multiphase nature of the blends does not provide optical clarity. European patent application, EP-443432-A, provides polymeric blends of thermoplastic polyurethane elastomers with graft elastomers consisting of butadiene or C.sub.1-10 alkyl acrylate cores crosslinked or graft linked to alpha methyl styrene, (meth)acrylonitrile and or methyl methacrylates. Many examples of TPPUE blends exist in the art, but few exhibit clarity.
Achieving TPPUE blends with useful heat distortion temperature characteristics also has been a problem. For example, polymeric blends disclosed in U.S. Pat. No. 4,141,879 comprise a polyamide homo- or co-polymer and a polyurethane reinforced with a relatively small amount of glass fibers, were disclosed possessing high heat distortion temperatures and utility for under-the-hood automotive or truck components, but these multi-component systems are prone to phase separation due to poor compatibility.
Thus, problems exist in achieving toughness and related mechanical properties, stable color, clarity, and higher heat distortion temperatures in TPPUE's and blends containing TPPUE's. The present invention teaches new compositions and their preparation and use in overcoming one or more problems with known materials by providing compatible or miscible blends, many of which are clear blends, containing TPPUE and one or more copolymers containing N-vinyllactam.